1. Field of the Invention
The present invention relates generally to monitoring the position of a beam, and more particularly to monitoring the position of a high energy beam used for patterning surfaces for electronic device manufacturing.
2. Background of the Invention
Pattern placement poses a critical problem in the electron-beam based manufacture of masks for proximity X-ray lithography, for photon beam-based reproduction of masks onto semiconductor wafers, and other devices used for manufacturing electronics. Lithography for 130 nm ground rule demands a 3"sgr" placement accuracy of better than 12 nm. For an x-ray mask, this placement accuracy is required over the entire mask, on the order of 10 cm2 in area, and containing many 100""s of millions of individually addressed pixels written at rates on the order of 1 MHz, or above. Unfortunately, several factors contribute to errors in the image placement. Although the absolute position of the stage can be maintained by means of laser interferometry, the same cannot be said of the beam. Instead, beam position is presently maintained as a xe2x80x9cbest effortxe2x80x9d, by active control of column element temperature and column electrode potentials, and periodic references to an off-membrane fiducial grid.
The device described in U.S. Pat. No. 5,703,373, issued Dec. 30, 1997, the entirety of which is incorporated herein by reference, addresses this problem by providing a beam detector and integrated fiducial grid which may be used under a transmissive membrane for position monitoring. In that device, a grid of wires or an apertured absorber layer is supported upon a uniform and intact Schottky contact layer. The grid or apertured absorber layer modulates an incident beam transmitted through the mask. That device, although useful, causes some backscattering of the incident beam due to the high atomic number of the materials in the grid or absorber layer. Because grid materials with high atomic number are required to achieve the needed absorption, that device, as designed, cannot avoid backscattering. Additionally, the need for establishing an electrical contact with the upper surface of the device prevented the device""s placement directly against the membrane. Because the transmissive membrane (e.g., a mask) causes forward scattering, and thus divergence of the incident beam, the separation between the transmissive membrane and the absorber layer/grid decreases the potential accuracy of the device.
Accordingly, it is an object of this invention to monitor the position of a high energy beam (such as an electron beam, a uv beam, an x-ray beam, etc.) with a device that results in minimum backscattering of the incident beam.
It is another object of the present invention to increase the accuracy in the formation of patterns using high energy beams.
It is an object of some embodiments of the present invention to allow a fiducial grid for beam monitoring to be placed in physical contact (zero-clearance) or near physical contact (clearance at or below about 10 xcexcm) with the backside of a transmissive membrane being patterned by the beam.
These and additional objects of the invention are accomplished by a semiconducting substrate having an upper surface with a diode layer thereon. The diode layer may be one or more diodes each of which surround a non-diodic region of the diode layer (i.e., a region on the upper surface of the substrate that does not include a depletion layer), or may be a known (predetermined) pattern of diodes which causes the surface to have distinct diode regions and non-diodic regions. Each diode is defined by an interface that forms a depletion layer within the substrate. When struck by an incident particle, the diode or diodes produce a detectable current. By comparing actual changes in current during the relative movement between the beam and the substrate or workpiece with the anticipated changes in current based upon the pattern and the expected relative movement between the substrate or workpiece and the beam, the error in beam position can be determined. Using simple and known algorithms (such as Fourier transform techniques) appropriate for feedback compensation, these errors can be corrected.